The present invention generally relates to medical devices and to ablative atherectomy burrs in particular.
Vascular diseases, such as atherosclerosis and the like, have become quite prevalent in the modem day. These diseases may manifest themselves in a number of ways, often requiring different forms or methods of treatment for alleviating the adverse effects of the diseases. Vascular diseases, for example, may take the form of deposits or growths in a patient""s vasculature which may restrict, in the case of a partial occlusion, or stop, in the case of a total occlusion, blood flow to a certain portion of the patient""s body. This can be particularly serious if, for example, such an occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids.
To treat these diseases, a number of different therapies have been developed. While effective invasive therapies are available, noninvasive therapies and minimally invasive therapies are desirable for many applications because these therapies generally decrease the chance of infection, reduce post-operative pain, and require less post-operative rehabilitation. Drug therapy is one type of noninvasive therapy developed for treating vascular diseases. Clot-busting drugs, for example, have been employed to help break up blood clots that may be blocking a particular vascular lumen.
Minimally invasive intravascular treatments exist that physically revascularize lumens. Two examples of such intravascular therapies are balloon angioplasty and atherectomyxe2x80x94both of which physically revascularize a portion of a patient""s vasculature.
Balloon angioplasty is a procedure wherein a catheter is inserted into a patient""s blood vessel through a relatively small puncture, which may be located proximate the groin. The catheter is intravascularly navigated by a treating physician to the occluded vascular site. The catheter includes an inflatable balloon or dilating member, which is placed adjacent the vascular occlusion and is then inflated. When the occluding deposit is relatively pliable, intravascular inflation of the dilating member, typically to a pressure on the order of 5 to 12 atmospheres or so, causes the balloon to displace the occluding matter towards the vessel walls and thereby restore substantially normal blood flow through the treated portion of the vasculature. It should be recognized that this procedure does not remove the matter from the patient""s vasculature, but displaces and reforms it.
While balloon angioplasty is frequently successful in revascularizing vascular lumens by reforming the occluded material, some occlusions are not amenable to treatment with this procedure. For example, some intravascular occlusions are composed of an irregular, loose, or heavily calcified material which may extend relatively far along a vessel or may extend adjacent a side branching vessel, and thus may not be prone or susceptible to angioplastic treatment. Even if angioplasty is successful, there is a chance that the occlusion may recur. Recurrence of an occlusion may require repeated or alternative treatments given at the same intravascular site.
Another class of minimally invasive, revascularizing devices has been developed that physically removes at least a portion of the material occluding a vascular lumen. Such treatment devices, sometimes referred to as atherectomy devices, use a material removal instrument, such as a rotating cutter or ablater, for example, to remove the occluding material. The material removal instrument is typically attached to the distal end of a flexible drive shaft that extends from an electric motor or compressed-gas-driven turbine through the patient""s vasculature to the site of the occlusion.
In operation, the drive shaft, which is covered with a nonrotating catheter for most of its length, is advanced over a pre-inserted guide wire until the material removal instrument is positioned just proximal to the occluded site. The motor or turbine then rotates the drive shaft and the material removal instrument as the material removal instrument is moved transversely through the occluded portion of the vessel. The material removal instrument removes the material from the vessel rather than merely displacing or reforming the material as in a balloon angioplasty procedure.
Ablative atherectomy devices use a rotating ablation burr to remove occluding deposits in the patient""s vasculature. The ablation burr is typically a small, ellipsoidal burr having an abrasive outer surface that is passed through the site of the occlusion while rotating at relatively high speeds, generally 50,000 to 200,000 rotations per minute. It has been found that healthy vascular tissue is pliable enough to resist ablation by the burr, but atherosclerotic plaques are less pliable and therefore are selectively removed by ablation.
With any atherectomy device, it is desirable to reduce the irritation and collateral damage to healthy vascular tissues during an ablation atherectomy procedure. In U.S. Pat. No. 6,015,420 to Wulfman et al., which is commonly owned by the assignee of the present application, an ablation burr is disclosed that has an abrasive coating only on a portion of the burr that is disposed radially inwardly from the burr maximum diameter, and therefore substantially prevents the abrasive portion of the burr from contacting the vessel walls. It has been found, however, that in some circumstances it can be difficult to move the burr transversely through heavily occluded vessels.
Given the above-discussed considerations, it is desirable to provide an atherectomy device having an ablation burr that can reduce irritation to the vessel walls while also facilitating moving the burr through the occluded region of the vessel.
The present invention overcomes many of the disadvantages of the prior art by providing an ablation burr for a rotational atherectomy device that reduces the risk of damage to a vessel wall while providing an ablative surface that has a diameter substantially equal to the maximum diameter of the ablation burr. The ablation burr according to the present invention utilizes two abrasive surfaces that are disposed on a leading portion of the burr body, a less aggressive abrasive surface is disposed on a portion of the burr nearest the vessel wall, and a more aggressive abrasive surface is disposed on a portion of the burr that is generally disposed further away from the vessel wall.
According to one embodiment of the present invention, the ablation burr has a smooth back surface and a leading surface wherein the leading surface has a first portion near the burr maximum diameter that is less abrasive and a second portion closer to the burr axis that is more abrasive.
In one aspect of the invention, the abrasive surfaces are composed of abrasive particles such as diamond affixed to the burr body. In another aspect of the invention, the abrasive surfaces are formed by etching, micromachining, or otherwise roughing the surface of the burr body.
In one embodiment of the present invention, the less abrasive first portion of the leading surface of the burr is generally convex and the more abrasive second portion of the leading surface is generally concave.